Introduction: Shooting for Photogrammetry
Being able to create something 3 dimensional from 2 dimensional photographs is definitely magical, but it can also take quite a bit of finesse to get the right kind of photos. In this sense, a large part of learning how to scan with photogrammetry is about learning basic photography and lighting technique, so I highly suggest also checking out audreyobscura'sPhotography Class for some great foundational information about camera operations and lighting.
Photogrammetry requires a very specific kind of photography, the aim of which is much more practical than aesthetic. Ideally every area of the object will be visible in at least two photos in order to give the reconstruction software enough points of reference to work with. There are a few different strategies you can use for your photo set-up depending on what kind of object you are shooting and your budget.
In this lesson, we'll talk about everything you need to know to shot your photos in different environments.
Step 1: The Two Shooting Strategies
As I've mentioned there are two basic strategies when you are shooting for photogrammetry: you can either shoot by moving your camera around an object, or rotate the object while keeping your camera still. I'm going to show you both.
A lot of sources will tell you that shooting around an object is the most effective, because reference points in the background help the software properly orient your photos in space. In my experience, however the other method produces much better results when done properly. It requires somewhat more careful preparation and more equipment, but it allows you far more control over your lighting and shooting environment.
When you shoot a rotating object, you need your background to be perfectly blank or featureless. This means you will need a black or white backdrop that is big enough to allow you to shoot your object from both high and low angles. You will also need a tripod, a turntable and usually some kind of artificial lighting set up to light your object and create perfectly blank background with no shadows.
Sometimes using this method will be impossible (say, if you want to capture a statue in an outdoor park) so depending on the object you are shooting and the equipment you will have available to you, you will have to choose for yourself which shooting method makes the most sense.
Getting either method right may require some trial and error, so try not to get discouraged. When I first started experimenting with photogrammetry, I was using the "shoot around an object" method, and I was having a lot of trouble getting good results. Eventually I switched to the "rotate the object" method, which worked a lot better for me, but some people have gotten great results from shooting around an object even with only a camera phone.
Step 2: Preparing Your Object for Scanning
Depending on what kind of object you've chosen to scan, you may need to make a few preparations before shooting. As I mentioned in the last lesson, the easiest objects to scan with photogrammetry are stationary medium sized objects with a matte finish, a good amount of surface detail and not many thin delicate bits. So, if you've decided that you really want scan the large shiny tuna fish you saw swimming at the aquarium, or a tiny delicate flower with 27 petals... you might just want to re-think that decision.
If you have chosen something a bit more rational (such as, say, the mind blowingly natural fractal geometry of this romanesco) you will still need to make sure you have your object set up correctly so you get the best possible photographs.
It's often helpful to fixture your object in a certain position before photographing it. For example, If you have an object that you want to scan all the way around, put it on a mount that holds it above the surface you are scanning on. An easy way to do this for an object like my romanesco, is to simply take a board or piece of plywood and hammer a long nail or piece of stiff wire through the center. Then you can stick your object onto the nail like this. (Just be careful if you leave this spikey booby trap lying around. I drilled a hole in another piece of wood to cover my nail when I wasn't using it).
Depending on what sort of object you are scanning, you might need to construct a different kind of stand. Another good option is to use a small tripod with a clamp so you can clap your object or clap a nail that you stick into your object. Sometimes you might not even need to capture the underside of your object, in which case a stand might be unnecessary.
If you are trying to shoot an object that has some undesirable characteristics for scanning, there are a few things you can do to make getting a good scan more likely.
If your object is shiny reflective or transparent: if you need to be able to return the object to its original state, try spraying it with a removable chalk spray paint. If you don't mind altering the object irreversibly, you can use a regular spray paint or brush on paint, just make sure you use something that is matte not glossy. Even small shiny areas on an object can sometimes cause problems in reconstruction, but sometimes just covering these areas up with carefully placed pieces of masking tape can help a lot.
If your object doesn't have a lot of surface detail: objects that are all one uniform color sometimes don't have enough points of reference for photogrammetry to use in reconstruction. So,if you are scanning an object like this mannequin head and you don't care about capturing the color layer, you can add your own details by drawing on the surface, or sticking stickers or pieces of tape on the object.
If your object is very small: if you determined to try scanning a very small object, you will need a camera with a very good macro lens and a tripod so your images come out extremely sharp. In fact, for extremely small objects, you may need to automate the process like Shapespeare did in this great Instructable.
If your object is large: if you really want to tackle scanning a large object, there are a few specific strategies that will help make this easier, and I will address some of these later in this lesson. A lot of people also use camera equipped drones to capture landscapes or buildings. To learn more about how capturing landforms with photogrammetry from the air check out this awesome instructable by moon_goose.
If your object is moving: it is impossible to scan objects that are actually in motion, but if you want to scan something like a human who has the potential to stand still, I will talk about strategies for this in the section on Scanning the Human Body.
Step 3: Lighting a Rotating Object
No matter how you are going to shoot your object, lighting is key. Low light or intense contrast will confuse the software, so strong diffused light works best. When you are shooting by keeping your camera still and rotating your object, you only need to light the part of the object that is facing your camera in any given shot. But you also need to make sure you are not casting light on your backdrop in a way that creates odd shadows or highlights. The background in these types of shots needs to be perfectly featureless or it will confuse the photogrammetry software.
To get really good results every time with this method, you will usually need to create your own lighting set-up. It can take anywhere from 1-3 diffused lighting sources to effectively light your object. There are a lot of options for this, but you can create an easy and fairly cheap one by following the instructions in audreyobscura's Photography Class.
Here's what you'll need:
Shine one of these lights on either side of your object from the front, adjusting them so they cast a diffused light with a perfectly even background. You may need an additional light shining down from above to catch the top of your object. You can also use a ring light that fits around your camera lens and shines on your object from the front. Just be sure you aren't casting any weird shadows as your object rotates. If you are using a white sweep you usually wand to shine a lot of light on the background, if you are using a black sweep, keep light on the background to a minimum.
Step 4: Shooting a Rotating Object
Once you have your object prepared and fixtured, place it on our turntable in front of your sweep and set up your lights so you are lighting the front of your object and creating featureless background.
For either shooting method, what you want to do is capture a series of overlapping photos all the way around your object at several angles. In order for photogrammetry software to reconstruct any point on your object, that point needs to be visible in at least 2 photos, so you need to shoot a lot of photos to capture an object well, anywhere from 20-250 depending on the size and complexity of your object. If you are shooting a very complex object you might need to shoot three or four rows of photos all around the object and some vertical rows from top to bottom. For a simpler object you might only need two rows total.
Set up your camera on a tripod in front of your object at an angle that you think will capture some important details. Make sure your object is filling up most of your frame, but not being cropped anywhere. Remember you are going to be spinning your object, so if it's an odd shape the framing could change as it rotates.
If you are shooting with a camera that allows you to adjust the settings, and you know how to use them, there are a few things you can do to optimize your images. You want to get as much of our object as possible in focus in every shot, therefore you want to shoot with a long depth of field. To do this, you need to set your F-stop to a high number, F8 is usually a good choice. A high F-stop means the aperture of your camera is smaller, letting in less light (confusing, I know). The less light you are letting in, the darker your photos will be, so you may need to proportionally slow your shutter speed to increase the brightness of your photos.
As you can see, it's a bit of a balancing at to get the right exposure. If your camera has an 'aperture priority' setting, that can be a good one to use, instead of full manual. This setting lets you set the desired F-stop, and then adjusts the rest of the camera settings accordingly.
Once you have everything set up, it's time to capture your object. Shoot one photo, then rotate your object very slightly on the turntable, about 5-15 degrees, and shoot another photo. Keep doing this all the way around until you are back to where you started. Make sure you are moving your hand fully out of the way for each photo so you don't create shadows, and watch for changes in lighting as you shoot.
Next, move your camera on your tripod to a higher or lower angle and repeat the same process. You need to capture every area of the object, especially any crevices, overhangs or details. Sometimes you also need to shoot a few vertical rows to get the bottom and top of the object. If your object has a lot of really fine textural details that you want to capture, you can also shoot some very close up detail shots to capture those.
Step 5: Lighting for Shooting Around an Object
If you are shooting by moving around an object, a lot of the same lighting rules apply. You always want diffuse even light, but this time you need the light to be even all the way around your object, which can be trickier to achieve.
With this type of shooting, working outside on an overcast day is particularly ideal, and more feasible since you don't need a blank backdrop.
If you need to shoot indoors, it is sometimes possible to find a good existing lighting situation. Look for places with bright even light and avoid rooms with windows. Having in a bright window appear in the background of some shots can change the exposure of your object and confuse the software. Places like grocery stores and some well-lit office buildings will sometimes have just the right kind of light, but a lot of indoor areas will be too dim, or have light that is too directional.
If you decide to use additional lights for shooting indoors, you will need at least 3, and sometimes 4, diffused lighting sources that you can use to strategically light all sides of your object evenly at once. The diffused clip lights from audreyobscura's Photography Class are again very useful here.
Your lights should be set up around your object so they cast an even light with minimal shadows. Try to position them close enough to shine as much light as possible one the object, but far away enough that they won't appear in your shots. This is hard to achieve, which is part of why I don't prefer this shooting method. It's almost impossible for the lights to not end up in some of your shots. It's not the end of the world if they do, but is not ideal.
Step 6: Shooting Around an Object
If you can, it's usually helpful put what you are shooting up on a stool or pedestal in the center of an open space to elevate it to a comfortable level for photos, which also makes it easy to walk around. Make sure you are shooting in a location where there is nothing moving in the background, as this will confuse the software. Also avoid places with a lot of shiny or reflective objects in the background.
It helps to have a distinct visual pattern around your subject. This provides more reference points for the software. It also means you'll end up with some extra bits under your 3D model, but these can be erased in the editing process. If you can find an object outdoors with a pattern around the base, it will be a huge help. The pattern of bricks under this fire hydrant really made it turn out well.
Or if you are indoors, just laying a piece of newspaper on your base or placing some small objects around it is enough, but make sure whatever you're using isn't shiny or reflective... I'm sure you're getting the point by now that shiny and reflective is the enemy of photogrammetry :)
You can try shooting your object either with or without a tripod. A tripod will ensure that all the photos in each rotation around your object are taken at the same angle. It will also help make your images sharp, especially if the light is low, but shooting with a tripod is also more time consuming so if you have bright enough light you might want to try shooting freehand first. Using monopod is a good compromise here.
The same camera setting suggestions apply here as for the other shooting method, and it can be especially useful here to have your camera on a manual setting so your exposure doesn't change as you move around your object. If you are shooting without a tripod, however be careful because a slow shutter speed, anything below about 60, can make your photos blurry, which is why lights and a tripod can help.
Choose an angle and start shooting by moving around your object, moving about 5-15 degrees for each new photo. Try to hold your camera as steady as possible and maintain the same angle all the way around until you are back to where you started. Then choose a higher or lower angle and repeat the same process.
Shoot as many rows as you think you need to capture your object, and make sure you get all the way over the very top. I find that it's easy to miss this part of the object which can result in scans like this:
Step 7: Tips for Scanning a Human
One thing that a lot of people want to do when they start out with 3D scanning is scan themselves or someone else. This is definitely a challenge, but it's not impossible. For one thing, humans are not static, so it's difficult to take all the photos you need for photogrammetry without your subject moving. Also, people are big, so you can't just put them on your little rotating turntable and call it a day.
The absolute best way to capture a person with photogrammetry is to create a multi-camera rig, so that images of the person are captured from all angles at the same moment, eliminating the problem of movement. Mparker07 as a great Instructable that shows how to create your own rig like this, the only problem is, it costs quite a bit of money to set up.
The cheapest way is to try shooting around your subject in even bright light like you did with the smaller objects. I've seen scans like this turn out quite well, you just need a really patient subject who is good at standing still. We were joking the other day that someday people will look back on 3D scanning today the same way we think of photo portraits from the 1800s: "Can you believe you had to stand still for so long just to be 3D scanned??!" :)
If you want to try the 'rotate the object' method of scanning a human, you will need an automated turntable, a large white or black sweep and some very good lights. You can put your camera on burst shooting mode with a very fast shutter speed and just shoot continually as your subject rotates. In my experience however, this method is more trouble than it's worth when scanning people, and doesn't get better results than the 'shoot around' method.
You can also check out this Instructable by Amy Karl for more info about human scanning.
Step 8: In the Next Lesson...
Once you have a good set of photos of the object you want to scan the hard part is over. In the next lesson I'll show you when and how to edit the photos you've shot, and then walk you through the process of uploading them to ReCap Photo where they will magically be transformed into 3D models!